1. Field of the Invention
The invention relates to a coil unit, a non-contact power transmitting apparatus, a non-contact power receiving apparatus, a vehicle, and a non-contact power supply system.
2. Description of Related Art
As described in Japanese Patent Application Publications Nos. 2003-79597 and 2008-67807 (JP-A-2003-79597 and JP-A-2008-67807), coil units have already been used in magnetic resonance imaging apparatuses. In recent years, focus is placed on pure electric vehicles and hybrid vehicles as an interest in the environment is growing and as a result, charging methods, such as an electromagnetic induction method and a resonance method, in which a coil unit is used, is attracting attention as a candidate of the charging method, in which a battery mounted on a vehicle is contactlessly charged by an external source.
A non-contact power supply system described in Japanese Patent Application Publication No. 7-67270 (JP-A-7-67270), for example, includes a primary coil buried in the ground and a secondary coil mounted on a vehicle, in which a battery mounted on the vehicle is charged using a current induced in the secondary coil.
A wireless power transmitting apparatus described in Japanese Patent Application Publication No. 2010-73976 (JP-A-2010-73976) includes a power receiving device that is mounted on a pure electric vehicle and that includes a power receiving communication coil, and a power supply apparatus that includes a power transmitting communication coil and the power receiving device includes a power receiving communication coil. The power transmitting communication coil includes a primary coil and a resonance coil and the power receiving communication coil includes a primary coil and a resonance coil. Between the power receiving communication coil and the power transmitting communication coil, electric power is wirelessly transmitted through a resonant power transmitting method.
The distance between a primary coil and a secondary coil, between which electric power may be transmitted by the non-contact power transmitting method using electromagnetic induction, is small and this method therefore requires that the primary coil and the secondary coil be positioned close to each other. Accordingly, this power transmitting method is unsuitable when electric power is to be transmitted or received beyond a certain distance. However, in the wireless power transmitting apparatus described in JP-A-2010-73976, a resonant power transmitting method is used and therefore, electric power may be transmitted or received over a greater distance than in the case of the electromagnetic induction method.
Even if the power transmitting apparatus employs the resonant power transmitting method, however, when the power transmitting resonance coil and the power receiving resonance coil are misaligned, both power transmission efficiency and power reception efficiency are significantly decreased.